Fix feeds

Update of RSS and Atom feeds to match standards.
* [RSS documentation](http://cyber.law.harvard.edu/rss/rss.html)
* [Atom documentation](http://tools.ietf.org/html/rfc4287)

## Changes:
* Updated self link to point site.JB.atom_path instead of  site.atom_path.
* Updated date formats to RFC 3339 for Atom and RFC 822 for RSS.

## Sources:
[http://cyber.law.harvard.edu/rss/rss.html](http://cyber.law.harvard.edu/rss/rss.html)
[http://pixelcog.com/blog/2013/jekyll-from-scratch-core-architecture](http://pixelcog.com/blog/2013/jekyll-from-scratch-core-architecture/#rss-and-atom-feeds)
[http://validator.w3.org](http://validator.w3.org)
[http://www.w3.org/2005/Atom](http://www.w3.org/2005/Atom)